As one type of vehicle drive devices, there is a vehicle drive device of the type that is provided with an electric motor, a differential gear for distributing and transmitting the power output from the electric motor to right and left drive wheels, and a clutch for making intermittent the coupling which is able to transmit the power between the differential gear and the electric motor. The vehicle drive device of this type is designed to discontinue the coupling state in which the power transmission is possible between the electric motor side and the drive wheel side while the electric motor for driving the drive wheels is stopped from being driven.
Further, as one type of front-and-rear wheel drive vehicles, there is a front-and-rear wheel drive vehicle which is provided with a prime drive device for driving prime drive wheels and a secondary drive device for driving secondary drive wheels and which is brought into a single drive traveling state of the prime drive wheels by the operation of the prime drive device or into a front and rear dual wheel drive traveling state by the operations of the dual drive devices including the prime drive device and the secondary drive device.
In the front-and-rear drive vehicle of this type, it is preferable that the coupling between secondary drive means and a drive power transmission path for the secondary drive wheels is kept disconnected in the single drive traveling state of the prime drive wheels by the operation of the prime drive device, and generally, there is taken a construction that a clutch is incorporated into drive power transmission means which couples the secondary drive means with the secondary drive wheels.
As the clutch for this purpose, there is used any of clutches of various kinds such as an electrically operable electromagnetic clutch, a pressure-type clutch which is operable under pressure such as hydraulic pressure, pneumatic pressure or the like, a mechanical clutch operable to be driven by secondary drive means. Of these clutches, a mechanical clutch may be chosen for the reason that any drive circuit of electric, hydraulic or pneumatic type is unnecessary, and a two-way clutch may be chosen for the reason that it has the function to perform the coupling and uncoupling in the both traveling directions including the forward traveling direction and the reverse traveling direction of the vehicle. Where the two-way clutch is chosen as the clutch, the secondary drive means and the secondary drive wheels are coupled by drive power transmission means incorporating the two-way clutch therein, thereby to constitute the secondary drive device.
In the front-and-rear wheel drive vehicle of this type, where the vehicle is provided with the secondary drive device incorporating the two-way clutch, the same is kept in the uncoupling state irrespective of the traveling direction of the vehicle during the single drive traveling by the operation of the prime drive wheels. Further, during the front and rear dual wheel drive traveling, the two-way clutch is brought by the secondary drive means of the secondary drive device into the coupling state for the vehicle traveling direction to transmit the drive power from the secondary drive means to the secondary drive wheels.
That is, during the front and rear dual wheel drive traveling, the front-and-rear drive vehicle is placed in the forward traveling state by driving the secondary drive means in the positive-going direction and is placed in the reverse traveling state by driving the secondary drive means in the reverse direction. In this case, the two-way clutch is kept in the coupling state for the forward traveling direction by the operation of the secondary drive means in the positive-going direction, or is placed in the coupling state for the reverse traveling direction by the operation of the secondary drive device in the reverse direction. Thus, the front and rear dual wheel drive traveling can be done in either of the forward and reverse directions of the vehicle.
By the way, downsizing, lightening and reduction in cost are requirements in the foregoing vehicle drive device. The present invention is aimed to cope with these requirements, with a view at the place for the clutch to be arranged at and/or the downsizing of the clutch. That is, an object of the present invention is to improve the capability of being mounted on the vehicle, to simplify the suspension system, to improve fuel consumption and to realize reduction in cost by downsizing and lightening a vehicle drive device of the aforementioned type.
Further, in the foregoing front-and-rear wheel drive vehicle, during the single traveling by the prime drive wheels, the secondary drive means is in the out-of-operation state, and the two-way clutch is held in an intermediate zone of the coupling states for both of the forward and reverse traveling directions. Thus, when the vehicle repeats the forward traveling and the reverse traveling in this state, the two-way clutch tends to generate dragging torque thereby to cause energy loss. Additionally, by the cause of the dragging torque generated in the two-way clutch, a problem arises in that the two-way clutch is brought into the coupling state, whereby the energy loss is further increased and whereby the drive torque of the secondary drive wheel side is transmitted to the secondary drive means side. Accordingly, another object of the present invention is to cope with these problems.